Low pH / KH, what about CO2?

[jsiegmund]

Hi there! I have resetted my tank 2 months ago now, switching to Akadama as soil. From that point on, as expected, I have low PH / KH values.

Plants are doing ok, but some of the more difficult species (mainly pogostemon helferi and bacopa sp japan) are still having issues; dropping older leaves and slow growth. I also have some green spot algae and hair algae that keep coming back. Not in an alarming rate, but always there. As a reaction I've been boosting CO2 slowly and lowering the lights a bit, searching for a good balance.

I've done a pH profile today; looks like this:
- Before lights on: 6.5
- CO2 comes on at 9:30 AM
- Lights come on 11AM, full strength at 11:30. At that time, pH dropped to 6.10
- It stays stable throughout the day at 6.05 roughly.
- CO2 switches off 19:30
- At 20:00 lights dim again, night mode at 20:30.
- pH then starts rising again, settling off at 6.5 after a few hours.

So I do not have a 1 point drop at the moment. My KH is very low (around 1), should be because of the Akadama. The net contents of my tank is about 200L, I have a FX5 which should circulate around 2300 liters/hour, easily reaching a >10x turnover.

My tapwater is moderate I'd say, KH 8.5 / GH 7. I usually change water using a mix of 50/50 RO - Tap. The RO I remineralise with this stuff, ordered some Seachem Equilibrium as well. At the moment my water changes are about 20 - 25% (weekly). The mix is kind of a legacy from what I did before, I'm not sure if it's still appropriate.

For micro's and macro's, I dose Ferrdrakon, PO4 and NO3 separately using a dosing pump daily (macro's in the evening, micro's in the morning). No3 is usually at 20, PO4 somewhere at 0.5. I'm upping the PO4 a bit, again slowly.

So what I am wondering about: what would be good values to strive for? Is a 1 point drop in pH really what you want in this case, a pH of 5.5 seems a bit low. I read that larger water changes are conceived to be better in general, so I want to try going up to 40 - 50% from now on. Any pointers are highly appreciated

 

[X3NiTH]

I have zero to negligible KH, my tank pH before adding gas is around 6.3 (if I use strong aeration up until the point of injection I can get up to 6.5), I need to drop my pH to around 5.2 and hold it there for my drop checker to indicate a reading of around 20-30ppm of co2. If you don't have a drop checker I recommend that you get one as this will tell you whether you are injecting enough co2. Hair algae for me was a symptom of way too much light (TMC mini400 tile @ 100% 3cm from water surface and 30cm from substrate), so backing off on the light is a good idea especially if you're not sure of the co2 level.

 

[ceg4048]

My tapwater is moderate I'd say, KH 8.5 / GH 7. I usually change water using a mix of 50/50 RO - Tap. The RO I remineralise with this stuff, ordered some Seachem Equilibrium as well. At the moment my water changes are about 20 - 25% (weekly). The mix is kind of a legacy from what I did before, I'm not sure if it's still appropriate.

Hello,
You don't really need to do this. It complicates your life and has zero benefit for plants unless the tap water is high in herbicides.

Your symptoms describe a CO2 failure so perhaps look at increasing the injection rate if feasible and more importantly, look at how you are distributing the flow. That filter is certainly good enough but the standard outlet might not be doing you any favors, especially if it not oriented to best advantage.

So what I am wondering about: what would be good values to strive for? Is a 1 point drop in pH really what you want in this case, a pH of 5.5 seems a bit low.

Why? Neither fish nor plants really care about this number and in any case, if you stop using RO then this won't be an issue.

As mentioned by X3NITH, reduce your light intensity, at least in the short term until you can sort out the CO2//distribution.

Cheers,

 

[jsiegmund]

Right, so your reactions are telling me I'm sort of on the right path, that's good

As for the details I missed: I've got a drop checker, but it's still pretty dark at the moment. My CO2 changes are slowly pushing it towards light green but I'm not there yet. I had no clue about the low pH, if going down to 5 isn't a problem for fish I'm going to try to acheive that 1 point drop. It does mean I have to add serious amounts of CO2, isn't that weird in combination with low pH/KH? Another thing I considered is adding some liquid carbon before lights on (have 1 dosing pump left). Would that be overkill or a good idea?

The CO2 is being dissolved in an external reactor, AM1000. At the moment that is still running of my old filter as I'm adapting the nozzles to be compatible with the FX5 hosing / throughput. That's nearly done and the FX5 has been running long enough now to make the switch. With a bit of delivery luck I might be able to do that tomorrow, otherwise it'll be in two weeks time as next weekend is fully booked.

The output of the FX5 is a spraybar which is as long as the tank is. Actually I'm looking to saw off a tiny bit of the end module to I can add one additional module to make it really go from edge to egde. But at the moment, flow is pretty decent as well. The only thing I need to change is to get it a bit higher up as it's now sitting about 7cm below the surface.

Thanks for the pointers, good stuff and much appreciated.

 

[ceg4048]

It does mean I have to add serious amounts of CO2

Yes, CO2 is serious business. So take it slowly and always observe your fish.

if going down to 5 isn't a problem for fish I'm going to try to acheive that 1 point drop.

Yes, this is correct. Fish only care WHY the pH is low. They do not care that the number itself is low. See more in the post http://www.ukaps.org/forum/threads/whats-the-importance-of-kh.31225/#post-331273
So when you add CO2, if your fish get injured, it will be because of too much CO2 asphyxiating them, not be cause of pH 5.

If you have an AM1000, you can improve it's performance by removing all of those bio-balls inside the cylinder.
That's good having a spraybar in that configuration.

Cheers,